By John R. Platt
Few species have undergone as spectacular a recovery as the Mauritius kestrel (Falco punctatus). Forty years ago the birds were nearly extinct, with only four of the small falcons remaining in the wild. But intense conservation efforts over the ensuing decades paid off. By 1994 the population had grown to a few hundred birds, enough for the International Union for Conservation of Nature to reclassify the species from “critically endangered” to simply “vulnerable to extinction.” The birds have fared even better since then: by 2005 the population of Mauritius kestrels had soared to between 800 and 1,000 birds, more than had existed on their island home for more than a century.
But although the Mauritius kestrel has recovered, the factors that drove it nearly extinct remain. Mauritius—one of the several islands in the Republic of Mauritius, located in the Indian Ocean—is almost completely deforested and overrun by invasive species such as black rats (Rattus rattus), Indian mongooses (Herpestes javanicus) and feral cats. Deforestation started when people colonized the previously uninhabited island in the 17th century. Today none of the island’s primary forests—the kestrels’ original habitat—remain and 98 percent of the rest of the island’s woodlands have been converted into sugar cane plantations or are regularly cut down for lumber. The only unmanaged forests remaining are in the most inaccessible parts of the island.
So what’s a kestrel to do in the face of this human-caused habitat change? According to research published February 20 in Current Biology, Mauritius kestrels have, over the past 23 years, started breeding at a younger age. This allows them to still have the same number of offspring, but it also comes at a cost: The birds die younger, too. (The birds are intensively monitored, so the researchers had access to extensive data on birth and survival rates.)
The study compared two populations of birds. One group lived in areas with no native flora. The other lived in regions with more than 30 percent native plants. The first group died at much younger ages, but they also adapted their breeding strategies. “We found that birds from both types of habitat still ultimately produce the same number of offspring in a lifetime,” lead author Samantha Cartwright, a postdoctoral researcher at the University of Reading in England, said in a press release. “The strategy is a good one: Breeding when younger compensates for the increased risk of dying sooner.”
Cartwright said this “adaptive, plastic response is a testament to how resilient this species is,” but also called the adaptation a warning. As she and her fellow researchers wrote in their paper, “our results suggest that human activities can have a persistent effect on the life histories of wild organisms…. Given the ubiquity of human-induced habitat change, the patterns we report could be widespread but remain poorly documented due to the short-term nature of most studies that attempt to quantify only the immediate impact of habitat change on fitness traits.”
This new paper builds on an earlier study by most of the same authors (with the exception of Cartwright), which was published in January 2013 in Ecology Letters. The previous study found the female kestrels that grew up in poor habitats were forced to disperse farther distances to find their own nesting sites than the females living in better habitats. At the time the authors theorized that this energy expenditure might reduce the former’s fecundity (which the new paper disproves) as well as decrease their life spans (which appears to be the case). Previous studies have also shown that the kestrels have a fairly low genetic diversity. The current study does not examine that as a facet of the species’s overall health. The birds also suffered from exposure to DDT and other chemicals used in the 1950s and ’60s. There do not appear to be any recent studies examining the long-term effects of these chemicals on the kestrels.
One wonders if this life cycle change will be enough to keep the birds healthy in the long run. A survey conducted between 2011 and 2012 found that the population of Mauritius kestrels has dropped again, this time down to about 400 individuals, according to the nongovernmental organization BirdLife International, based in Cambridge, England. At least one subpopulation has disappeared since 2005 and others are shrinking. BirdLife reports only a single population is currently considered stable and that there is no genetic transfer between isolated groups. Obviously the successful recovery of the Mauritius kestrel remains fragile and the future of the species remains to be written.